Cuprous salt-hydroxyalkylamine solutions



OFF-GAS FEED IN V EN TOR. C. E. SMITH Www?? T TORNEYS OLEFlN-CONTAlNING 2,943,060` fPa't-:ntd Ju-ine 228, 196() Stages Patent ce The "utilization *of cuprous vsalts dissolved in a suitable liquid :mdium such 'as, for example, aqueous organic 5 bases 'or aqueous NH3, in proc'esses 'for the recovery of Y normally gaseous olein hydrocarbons, particularly ethylene or propylene, from .gase'ous 4hydrocarbon streams 'c' tining tl1em is conventional v'as stated above. In hes'e processes the 'oleins are dissolved "in the cuprous 10 .reagent vprincipally by Vformation of a soluble coordina- Y tion complex"with cuprous'ions. The vrecovery of the 'Q1 rmfthe Vcomplex` is'uSuallyfeHected by subjecting fthe listincontaining solutiontoV at leastone of the steps of pressure `reduction "and heating 'to `cause liberation Le udi'ss0-1ved olefin. Following liberation of the n theresultingolefnjdenuded saltsolutionmay be "then: used i No `absorb oleins from va fresh portion of SULUTIONS incontainin'gstream. i

icularly suitable reagents forsuch processes are t1onsof`tle .cuproussal'tsjsuch as, for example, cupros l itrate, cuprous chlorid and 'cuprous acetate in aqueous"'monoethano1aniine- Ho we\ ier the monoethano ly opper saltsolutions'-arefunstable"on v heating to "tem eratuie's "of the'orderof`8 0 C., 'Whicharedesirable J 1r) atisfattor-yv `desorption of thejhydrocarbons `from the When this reagent slheated tjo temperatures suc`1 ently` hightodesobjessentially, all of the complexed fleiing reactions pccurjwhch eventually lead to 'the Y Ae "addition of Vsuch ammonium salts Y gent during dissolution of fthe copper inthe art-Alfortheprep- Y larly a cuprous nitrate-monoethanolamine solution, of the present invention. An admixture of cuprous oxide or metallic copper with cupric oxide is added to a solution of ammonium nitrate and ammonium hydroxide containing an excess of the nitrate over the stoichiometric equivalentof the copper. The solution is heated `and stirred during the dissolution of the copper and ammonia is usually driven olf during this heating step.v Following dissolution of the copper, monoethanolamine is added to the solution while stirring andheatingat elevated temperature, e.g., 90 C., and heating is continued until no ammonia is given off. The cuprous nitrate reagent may also be prepared by dissolving a mixture of metallic copper and/or cuprous oxide with cupric oxide in a mixture of monoethanolamine, water, and ammoniurn nitrate. The ammonium nitrate is dissolved in the water and the solution mixed with the amine. The copper-copper oxide mixture is added to the solution and heat is applied so as to gradually raise the temperature to and hold it at about 70 C. The copper-copper oxide is held in suspension by constant stirring until all of it goes into solution. As the metal goes into solution ammonia is evolved, and stirring is'usuallyV continued until this evolution stops. The amount of total copper in `thereagents should be in the range of 8 tov l5 Weight percent, preferably l to .l2 weight percent of the solution. In accordance with the present invention, ammonia and/or an ammoniunrsalt is added to the cuprous salt-monoethanolamine solution after its preparation and after cooling to ambient temperature, whether by the above-described methods or by any other known method in the art, so as extend its useful life for the absorption olens.` The amount of ammonia and/ or ammonium salt added tothe reagent should beat least percent of the stoichiometric equivalent of the cuprous copper in the solution, i.e., 5 moles per 100 moles of cuprous copper. Amounts of 40 percent have been employed with excellent results.

Amounts up to 100 percent and higher can be used but Iwithout material improvement over a 40 percentconcentration based on the copper equivalent. While itis diicult to prepare the cuprous salt-ethanolamine solution with a suidcient ammonia and/or ammonium salt content to stabilize the solution by adding an excess of the same over that required to convert the copper to the cuprous salt and controlling the heating and copper solution step so as not to drive off all ofv the ammonia,. such a procedure may be followed to provide a reagent having a concentration of ammonia or ammonium vsalt equivalent to at least 5 percent of the cuprous copper. However, it is difficult to control the concentration of the NH4 ion by this method and, therefore, the step of adding the ammonia and/or ammonium salt after dissolution of the copper in the solution is much preferred.

The amount of cupric copper required in the solution is very small and usually should be in the range of about 1 to 2 or 3 percent of the copper content of the solution. However, even a trace suffices, but it is morepractical to maintain a concentration not too near the zero point so as to avoid possible copper deposition. Concentrations of 0.1 percent up to 20 percent of the copper 'content are operable. In preparing solutions in accordance with the invention, it is generally suflicient to use reagent grade cuprous oxide which generally contains enough cupric oxide to provide sufcient cupric ion. f

'Ihe cuprous salt reagents of the invention contain to 15, and preferably 10 to 12, weight percent Cu, from a trace up to 20 percent of which may be cupric copper, monoethanolamine (or other hydroxyalkylamine) .in the rangee of about 40 to 60 weight percent, waterA in the range of about 10 to 35 weight percent, and the balance the anion of the copper salt.

The cuprous reagents of the presentinvention are preferably contacted with the hydrocrbonlin' thelgaseous phase. Any suitable method of contacting the gaseswith the liquid solution ofcuprous salt maybe employed.

The preferred procedure is -to contact countercurrently the hydrocarbon in the gas phase with the liquid in a tower provided with bubble plates or other contact elements such as sprays, packing, baies, etc. Desorption of the olefns from the cuprous reagents can be elfected by subjecting the solution to at least one of pressure reduction or heating to cause liberation of the dissolved olefin. If desired, the olen can be removed from the solution by stripping with an inert gas such as isobutane, etc.

Better understanding of my invention will be obtained upon reference to the accompanying schematic flow diagram, which shows the utilization of my improved reagent, i.e., cuprous nitrate-monoethanolamine solution, for the recovery of ethylene from a hydrocarbon stream containing it.

Referring now to the drawing, a gaseous ethylene-containing hydrocarbon stream obtained from a source not shown is passed through line 10 to absorber 11. The feed gas is introduced near the bottom of absorber 11 and rises countercurrent to a cuprous nitrate-ethanolamine solution containing ammonia in a concentration of about 40 percent of the cuprous salt equivalent yand admitted by line 12. Thel ethylene is absorbed at elevated pressure in the cuprous nitrate-ethanolamine-ammonia solution, and the denuded gas is discharged by vent pipe Q13 from the top of absorber 11. AThe enriched Vcuprous nitrate ethanolamine ammonia solution'js withdrawn from the bottom of absorber 11 and passed rvia line 14 through heat exchanger 15v to the top of desorber 146 through which it passes downwardly countercurrent to astreamof isobutane supplied from line 17. The isobutane strips the absorbed ethylenefrom the cuprous nitrate-ethanolamine-ammonia solution and a mixture of isobutane and ethylene together with a small amount of ammonia, depending upon .the desorption conditions and especially the temperature, is taken overhead via line 18. If desired, the ethylene can be released in the desorberd by either applying heat and/or reducing the pressure. The lean cuprous nitrate-ethanolamine-ammonia solution is withdrawn from the bottom of desorber 16 via lines 19 and 20 and passed through heat exchanger 15, and then returned to the top of absorber 11. Make-up-cuprous nitrate-ethanolamine-ammonia solution is introduced through line Z1 as needed. The selective `absorptionis usually conducted at a partial pressure of v the ethylene of 1-100 p.s.i.a., preferably 15-90 p.s.i.a,

and at a temperature in the range of about 30 to 60 C., preferably 1050 C. Desorption as shown can be carried out at about atmospheric pressure and a temperature of about 25-60 C., preferably vL10-55C.

The gaseous mixture removed by line 18 from the top of desorber 16 comprises ethylene, isobutane, some ammonia, and water; and this mixture is passed through heat exchanger 22 wherein it is cooled so as to condense out some of the entrained water and ammonia, which is collected in accumulator 23. The ammonia and water l solution is advantageously recycled to the absorber by introducing it intothe lean solvent inline 21 via line 24. Make-up ammonia and/or ammonium salt may be introduced to the absorber, as needed, via line 21 or by means of a separate inletline (not shown). Ethylene and isobutane partially denuded of water and ammonia removed :from accumulator 23 is passed via line 2S to water Wash withfdilute sulfuric acid, or by other suitable means.'

` prepared as *follows In one case `42h covered fin separator 28 and recycledvia "line :30 and `added-to the leanabsorbentlinline'20. :Gperatingias set for the above, very little ammonia, if any, is lost rand consequentlythe reagent can ibeused for a'long [time Without any copper deposition. "The washwte'iracontaining some ammonia is recycled :to the washftowerviailinef'l.

Make-up water is added via line 32 as needed. i A

A series of thermalrstabilityftests Wasmade .oncuprous i 4the equilibrium-Gui-@CuH-l-Gu. As long-as :ajjsmall amount, such as a trace, -of'the 'cupricion is present, -no w nreciptaton of -free coppenoccurs.

Dataare presented inthe ltable lbelow, comparing the. Ltime required 'for Cu++ removal, and subsequent-,freercopper deposition, from cuprous nitrate, cuprous lolglorigle,

and cuprous acetate solutions-*in monoetlranolamine at several temperatures :both with-and --without excess am- ',.rnonium salts added during the preparation `of theret agent, and withV 4excess *ammonia or -ammoniumhsalts Yadded according -to the present invention afterfpreparation of the reagent. i 5 l Ihe various cuprous saltsshown inthe table without anexcess )of yammonium"lion inthe final solutionV were in another, 59.5 grams NHgAc; and fm Lstill 3emot-lier, 62.5 grams of NH4NO3 were added to 250 cc. concentrated NH4OH. Then 45 grams Cu2O and 5 Vgrams CuO f were added to the ammoniacal solution. This solution was stirred and heated to a temperature of about 50 C. and held until the copper Ywent into solution. Following this step 250 cc. of monoethanolamine was added to the solution. Again the solutionV was stirred and heated to a temperature of about `90 C. and held lat .this temperature until there was no ammonia odor. Both the excess water and ammonia were removed in the second heating step. The cuprous chloride-monoethanolamine solution contained 1.84 weight percent cupric copper based on the total copper content, the acetate solution contained 1.17 weight percent, and the nitrate solution contained 1.47 weight percent cupric copper initially. The two cuprous nitratemonoethanolamine son lutions prepared with percent and 40 percentrexcess ammonium ion were prepared the same as above except that 72.6 grams NH4NO3 land 83.8 grams of NH4NO3 were used, respectively. The 20 percent excess' preparation contained 1.64 weight percent cupric copper, and the 'other 1.84 weight percent cupric copper.

The cuprous reagents containing 40 percent excess ammonium ion were prepared in the same manner as those prepared without an excess with the exception that Y either 40 percent excess NH4C1, NH4OH or NH4Ac Was added to the reagent after dissolution of the copper in the monoethanolamine and removal of excess 'water and ammonia.

From the data at 70 C. it can be -seen that the addition of an ammonium salt to the nitrate, chloride, or acetate solutions of cuprous copper, or the addition of NHOH in the case of the nitrate, increased Ythe thermal stability of the solutions 'materially/ For example, the life 'of the chloride solution wasrincreased almost ninefold, whilevthe life of thenitrate solutionwas doubled. It should be noted that theaddition'of NaNOa to the NO3 did not improve vthesta'hility,"but decreased .itj

Yns

details vdisclosed are not `to be construed as 'imposing'un- Y necessary limitations'onthe` invention. p

.f7-'1. iA process for preparing an improved'cuprousA saltalkanolamin'e solution which 'comprises forming a sol'ution comprising cupric Vion, Va cuprous jsalt,fand f*an weight percent Cu of which 0 .1' to 20' -percent is Y'clipric 'copper between 40 and 460 weight percent alkanolamine, between 10 -and 35 weight percent water, and' anion lof the cuprous salt; vand thereafter dissolving in said-solution atleast one member of the group ammonium acetate, ammonium chloride, ammonium nitrate, and -ammonium hydroxide in an amount in the 4range of 5 to 100 moles per moles of cuprous copper so as to increase the stability of said solution.

2. The process of claim 1 wherein the ammonium salt comprises ammonium nitrate.

3. The process of claim 1 wherein the lammonium salt comprises ammonium chloride.

4. The process of claim 1 wherein the ammonium salt comprises ammonium acetate. y

5. A process for preparing `an improved cuprous saltmonoethanolamine solutionwhich comprises dissolving cupric oxide and at least one member of the group conf sisting ofcuprous oxide and copper in a solution of an ammonium salt of the group Aconsisting of ammonium chloride, ammonium nitrate, and ammonium acetate in ammonium hydroxide; mixing with the resulting solution monoethanolamine; heating the resultingcuprous saltmonoethanolamine solution until ammonia ceases to Ibe driven olf, the resulting solution containing between 8 and 15 weight percentY Cu of which 0.1 to 20 percent is cupric copper, between 40 and 60 weight percent monoethanolamine, between 10 andV 35 weight percent water, and anion of said salt; and thereafter dissolving in the resulting solution at least one member of the group consisting of ammonium acetate, ammonium chloride, ammonium nitrate and ammonium hydroxide in an amount in the range of 2'() to 100 percent of the stoichiometric equivalent of the cuprous salt in said solution.

6. A process `for preparing an improved cuprous saltmonoethanolamine solution which comprises dissolving a mixture of cupric oxide and at least one member of the group consisting of cuprous oxide and copper in a mixture of monoethanolamine, water, and an ammonium salt of the group consisting of ammonium acetate,

Yammonium chloride, ammonium nitrate by heating and stirring the copper-containing mixture until evolution Vof ammonia ceases, the resulting solution containing be-V tween 8 `and Y15` weight percent Cu of which E0.1 to 20 -cent water, and anion of said salt; and thereafter dissolving in said solution at least one member of the group consisting of ammonium acetate, ammonium chloride, ammonium n itrate, and ammonium hydroxide in an amount in the range of 5 to 100 percent of the stoichiometrical equivalent of the cuprous salt in said solution.

7. The process of claim 6 wherein the ammoniumsalt in the rst step comprises ammonium nitrate and ammonium nitrate is added to the cuprous salt-monoethanolamine solution.

8. A stabilized solution of cuprous salt and alkanolamine of not more than 4 carbon atoms per'molecule containing between 8 and.15 weight percent C11 of which 0.1 to 20 percent is'cupric-copper, between 40 and 60 weight percent a1kanolaminebetween 10 and 35 weight tion of the copper salt in an amount inthe range of 5"to 100 percent .ofthe i stoichiometric equivalent. 4 of the cuprous salt, said solutionhaving greater stabilitythan before incorporating said ammonium lion therein.v p

9. The solution of claim j8wherein said alkanolamine comprises monoethanolamine.

10. The solution of claim 8 wherein the 11. The solutiontof claim Smwherein the ammonium 1 ion isincorporated inthe solution byv dissolving therein ammonium chloride.

l ammonium acetate.

13. The solution of claim 8 wherein the anion of the cuprous salt isNO'a and the ammonium ion is incorporated inthe solution by dissolving therein ammonium nitrate.

14; The solution of claim 8 wherein the anion of the cuprous salt is NO3 and the ammonium ion is incorpo- `rated inthe solution by dissolving therein `ammonium chloride.

' 15. The solution of claim 8 wherein the anion of the hydroxide and ammonium nitrate.

References Cited in the le of this patent UNITED STATES PATENTS 2,005,500 Joshua et al. June 18, 1935 2,235,119 Robey Mar. 18, 1941 2,245,719 `Robey June 17, 1941 2,376,239 l Evans et al'. May 15, 1945 2,383,784 Fleer Aug. 28, 1945 *2,429,134 Morrell et al. Oct. 14, 1947 y 2,445,520 Francis et al. July 20, 1948 2,494,546 FasceA Jan. 17, 1950 V2,561,822A vSavoy July 24, 1951 FOREIGN PATENTS 120,546 Great Britain Jan. 15, 1920 540,896 Germany Dec. 28, 1931 OTHER REFERENCES Handbook of Chemistry and Physics, 28th Ed., pages 338-343 and 376-382 (1944), pub. by Chemical Rubber v VPub. Co., Cleveland, Ohio.

UNITED STATES PATENT oEEICE CERTIFICATE OF 'CORRECTION Patent No., ZqllvOO June 28 1960 Clifford E., Smith s in the-printed specification It is hereby certified that error appear the said. Letters of the above 'rmmbered patent requiring correction and that Patent should read as corrected below.

Column 'L1 line los,l for "percent C11n rea d this 25th day of April 1961 i Signed and seele (SEAL) Attest: ERNEST W.. SWITDER tteeting Oiicer DAVTD L., LADD Commissioner of Patente UNITED STATES PATENT OFFICE CERTIFICATE 0F 'CORRECTION aaevoeo Patent No June 28 v 1960 Clifford E., Smith n the-printed specification tfed that error appears atent requiring correction and that the said.. Letters ted below.

It is hereby cer oi the above numbered p Patent should read as correo Column 7 q line 16v for percent C11" read f percent Cu n signed and sealed this 25th day of April Teer, V

(SEAL) Attest;

ERNEST W., SW'DER. DAVD L o LADD Commissioner of Patente ttesting Officer 

8. A STABILIZED SOLUTION OF CUPROUS SALT AND ALKANOLAMINE OF NOT MORE THAN 4 CARBON ATOMS PER MOLECULE CONTAINING BETWEEN 8 AND 15 WEIGHT PERCENT C11 OF WHICH 0.1 TO 20 PERCENT IS CUPRIC COPPER, BETWEEN 40 AND 60 WEIGHT PERCENT ALKANOLAMINE, BETWEEN 10 AND 35 WEIGHT PERCENT WATER, AND ANION OF CUPROUS SALT BEFORE ADDITION OF HEREINAFTER NAMED AMMONIUM ION, AND AMMONIUM ION INCORPORATED IN SAID SOLUTION AFTER COMPLETE DISSOLUTION OF THE COPPER SALT IN AN AMOUNT IN THE RANGE OF 5 TO 100 PERCENT OF THE STOICHIOMETRIC EQUIVALENT OF THE CUPROUS SALT, SAID SOLUTION HAVING GREATER STABILITY THAN BEFORE INCORPORATING SAID AMMONIUM ION THEREIN. 